Respiratory syncytial virus (RSV) is the leading cause of lower respiratory tract infections in infants and small children. RSV infection in mice is characterized by significant immunopathology which is mediated by CD8+ cytotoxic T lymphocytes (CTL). Past studies have suggested that CD8+ T cells with different functional properties and characteristics can be elicited following infection or immunization, and may have differential effects on viral clearance and RSV-associated illness. We have described differences between neonatal and adult CD8+ T cell responses elicited during RSV infection. Differences in clonotype, functional avidity, and other intrinsic parameters of the CD8+ T cell response may help dictate the epitope hierarchy established following infection. We are currently evaluating lung dendritic cell responses, and the elicitation of adaptive responses in both neonates and adults. This work has been greatly aided within the last year by the development of three strains of transgenic mice with CD8+ T cells specific for RSV. Continued work on this study will fully characterize CD8+ T responses to RSV, elucidate important factors that dictate the type of CD8+ T cell response that is generated, and help understand how other cell types regulate the CD8+ T cell response to result in either a beneficial or a detrimental effect.